Apparatus and method for reducing peak to average ratio in wireless communication system

ABSTRACT

The purpose of the present invention is to reduce the Peak-to-Average Ratio (PAR) of a transmission signal. A transmission device includes a generation part for generating a cancellation pulse corresponding to a peak component of a transmission signal, and a cancellation part for attenuating the peak component using the cancellation pulse. In addition, the present invention includes some embodiments other than the aforesaid embodiment.

PRIORITY

This application is a National Phase Entry of PCT InternationalApplication No. PCT/KR2014/011829, which was filed on Dec. 4, 2014, andclaims priority to Korean Patent Application No. 10-2014-0001768, whichwas filed on Jan. 7, 2014, the contents of each of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to reducing a Peak-to-Average Ratio (PAR)in a wireless communication system.

BACKGROUND ART

A Peak-to-Average Ratio (PAR) or crest factor of a signal is a ratiobetween an average level of the signal and a maximum magnitude of thesignal. FIG. 1 illustrates an example of a transmission signal in awireless communication system. A signal s(t) on a time axis is shown inFIG. 1. The PAR or the crest factor implies a ratio of a maximum value110 against an average level of the s(t). In general, the crest factormay be calculated in a dB scale. Therefore, the PAR or the crest factormay be given in a logarithm form of a ratio between an average signallevel and a peak.

If the signal has a high PAR, a high power amplifier is required whichoperates with large input back-off. Accordingly, amplification of thesignal having the high PAR is not effective in general. Therefore, thereis a need to propose an effective alternative for reducing the PAR.

DISCLOSURE OF INVENTION Technical Problem

An exemplary embodiment of the present invention provides an apparatusand method for reducing a Peak-to-Average Ratio (PAR) of a signal in awireless communication system.

Another exemplary embodiment of the present invention provides anapparatus and method for cancelling or attenuating a peak component of asignal in a wireless communication system.

Another exemplary embodiment of the present invention provides anapparatus and method for generating a cancellation pulse for cancellinga peak component of a signal in a wireless communication system.

Another exemplary embodiment of the present invention provides anapparatus and method for reducing a time of generating a cancellationpulse in a wireless communication system.

Another exemplary embodiment of the present invention provides anapparatus and method for generating a cancellation pulse by using asymmetry property of a basic waveform for the cancellation pulse in awireless communication system.

Solution to Problem

According to an exemplary embodiment of the present invention, anapparatus for a transmission device in a wireless communication systemincludes a generator for generating a cancellation pulse correspondingto a peak component of a transmission signal, and a cancelling unit forattenuating the peak component by using the cancellation pulse, whereinthe generator generates a first part which is a portion of thecancellation pulse, and generates a second part which is the remainingportions by using a symmetric property of a basic waveform for thecancellation pulse.

According to another exemplary embodiment of the present invention, amethod of operating a transmission device in a wireless communicationsystem includes generating a cancellation pulse corresponding to a peakcomponent of a transmission signal, and attenuating the peak componentby using the cancellation pulse, wherein the generating of thecancellation pulse comprises generating a first part which is a portionof the cancellation pulse, and generating a second part which is theremaining portions by using a symmetric property of a base waveform forthe cancellation pulse.

Advantageous Effects of Invention

Since a cancellation pulse is generated by using a symmetry property ofa base waveform for the cancellation pulse in a wireless communicationsystem, a time of generating the cancellation pulse is decreased.Accordingly, it is possible to process all of a plurality of peakcomponents which are continuously generated on a time axis.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an example of a transmission signal in a wirelesscommunication system;

FIGS. 2A to 2C illustrate a method of reducing a Peak-to-Average Ratio(PAR) in a wireless communication system according to an embodiment ofthe present invention;

FIG. 3 illustrates a block diagram of a means for reducing a PAR in awireless communication system according to an exemplary embodiment ofthe present invention;

FIGS. 4A to 4C illustrate an example of a result of processingcontinuous peaks in a wireless communication system according to anexemplary embodiment of the present invention;

FIG. 5 illustrates a characteristic of a base waveform for acancellation pulse in a wireless communication system according to anexemplary embodiment of the present invention;

FIG. 6 illustrates generating of a cancellation pulse by using a memorybuffer in a wireless communication system according to an exemplaryembodiment of the present invention;

FIG. 7 illustrates a block diagram of a means for generating acancellation pulse in a wireless communication system according to anexemplary embodiment of the present invention;

FIG. 8 is a conceptual view illustrating a procedure of generating acancellation pulse in a wireless communication system according to anexemplary embodiment of the present invention;

FIGS. 9A to 9E illustrate another example of a result of processingcontinuous peaks in a wireless communication system according to anexemplary embodiment of the present invention;

FIG. 10 illustrates a procedure of generating a cancellation pulse in awireless communication system according to an exemplary embodiment ofthe present invention;

FIG. 11 illustrates a procedure of operating a transmission device in awireless communication system according to an exemplary embodiment ofthe present invention;

FIG. 12 illustrates a block diagram of a transmission device in awireless communication system according to an exemplary embodiment ofthe present invention; and

FIG. 13 illustrates a simulation experiment result of a method ofreducing a PAR according to an exemplary embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described herein below with reference tothe accompanying drawings. In the following description, well-knownfunctions or constructions are not described in detail since they wouldobscure the invention in unnecessary detail. Also, the terms used hereinare defined according to the functions of the present invention. Thus,the terms may vary depending on user's or operator's intension andusage. That is, the terms used herein must be understood based on thedescriptions made herein.

Hereinafter, the present invention describes a technique for reducing aPeak-to-Average Ratio (PAR) of a signal in a wireless communicationsystem.

In the following descriptions, a signal may consist of complex numbers,for example, a real component and an imaginary component. The realcomponent may be referred to as an ‘I component’, and the imaginarycomponent may be referred to as a ‘Q component’. For transmission, thecomplex signal requires two separated wires, one of which is for the Icomponent and the other one of which is for the Q component. Therefore,even if a signal path is illustrated as one path in the figure describedhereinafter, it may be interpreted that the one path includes a path forthe I component and a path for the Q component.

Further, in general, the complex signals are expressed as a magnitudeenvelope. The envelope is a curve in contact with all curves having aregularity, and an envelope of a Radio Frequency (RF) signal indicates achange in a magnitude of a low-frequency component other than ahigh-frequency signal. Therefore, a signal illustrated in the figuredescribed below may be interpreted as an illustration of an envelope.

The PAR may be reduced by detecting a peak from a given signal and byattenuating or cancelling the peak. Accordingly, various exemplaryembodiments of the present invention describe a technique for reducingthe PAR by cancelling the peak.

FIGS. 2A to 2C illustrate a method of reducing a PAR in a wirelesscommunication system according to an embodiment of the presentinvention. Specifically, FIG. 2A illustrates an initial signal 210, FIG.2B illustrates a cancellation pulse 220 for cancelling a peak, and FIG.2C illustrates a peak-cancelled signal 230.

Referring to FIG. 2A, when the initial signal 210 is generated, a peak214 exceeding a pre-defined threshold 212 is detected from the signalthrough peak detection. Upon detection of a position and magnitude ofthe peak 214, as shown in FIG. 2B, the cancellation pulse 220 isgenerated in accordance with the magnitude and position of the peak 214.A specific waveform of the cancellation pulse 230 is pre-definedaccording to a signal characteristic of a system. That is, thecancellation pulse 220 may be generated by scaling a pre-defined signalpattern according to a complex gain which is in proportion to the peak214. Thereafter, the cancellation pulse 220 shown in FIG. 2B issubtracted from the initial signal 210 shown in FIG. 2A to obtain thepeak-cancelled signal 230 shown in FIG. 2C, that is, the signal 230 ofwhich a PAR is reduced.

FIG. 3 illustrates a block diagram of a means for reducing a PAR in awireless communication system according to an exemplary embodiment ofthe present invention. A block diagram of a device for reducing the PARby using the method shown in FIGS. 2A to 2C is exemplified in FIG. 3.

Referring to FIG. 3, the means for reducing the PAR includes a peakdetector 310, a Cancellation Pulse Generator (CPG) 320, and subtractors332 and 334.

The peak detector 310 is provided with I and Q components of an inputsignal, calculates a signal magnitude by using the I and Q components,and thereafter detects at least one peak. The peak implies signalsamples having a magnitude exceeding a threshold. That is, the peakdetector 310 detects a signal duration having a magnitude exceeding thethreshold from the input signal. Specifically, the peak detector 310detects a position of the peak and a magnitude of the peak. Further, thepeak detector 310 provides the CPG 320 with a complex gain correspondingto the position of the peak and the magnitude of the peak.

The CPG 320 generates a cancellation pulse for cancelling the peak. Aspecific waveform of the cancellation pulse is pre-defined according toa signal characteristic of a system. That is, the CPG 320 includes amodule for scaling a base waveform of the cancellation pulse accordingto the complex gain. The base waveform may be referred to as a ‘noiseshaping filter’. The module for performing the scaling may include atleast one complex multiplier. Accordingly, the CPG 320 multiplies thebase waveform of the cancellation pulse by the complex gain to generatethe cancellation pulse for attenuating or cancelling the peak detectedby the peak detector 310.

The subtractors 332 and 334 respectively correspond to the I componentand the Q component, and subtract the cancellation pulse from the inputsignal. Accordingly, the peak may be attenuated or cancelled from theinput signal. That is, the peak is cancelled as shown in FIG. 2C througha subtraction operation of the subtractors 332 and 334.

As shown in FIG. 3, when a peak exceeding a threshold is generated in aninput signal, the means for reducing the PAR according to the exemplaryembodiment of the present invention generates a cancellation pulsecorresponding to the peak and subtracts the cancellation pulse from theinput signal, thereby reducing the PAR of the signal. In this case, themeans for reducing the PAR processes peaks on a one-by-one basis. Thatis, the CPG included in the means for reducing the PAR is dedicated forone peak during one time duration, that is, during a specific timeduration.

The CPG may operate on the one-by-one basis for each peak, and mayprocess only one peak at any given moment. Accordingly, a cancellationpulse is generated also on the one-by-one basis, and for example, onlyone cancellation pulse may be generated at one time point. This impliesthat the cancellation pulse cannot overlap on a time axis. A new peakcannot be accepted until one peak currently being processed iscompletely processed. Due to the operation performed on the one-by-onebasis, a processing time for one peak is the same as a length of thecancellation pulse. For example, if the cancellation pulse includes Nsamples, a new peak generated within a time of the N samples cannot beaccepted. Accordingly, if a plurality of peaks are generatedcontinuously in a contiguous manner on the time axis, there may be adeterioration in peak cancellation performance.

FIGS. 4A to 4C illustrate an example of a result of processingcontinuous peaks in a wireless communication system according to anexemplary embodiment of the present invention. Specifically, FIG. 4Aillustrates an initial signal 410, FIG. 4B illustrates cancellationpulses 420-1 and 420-2, and FIG. 4C illustrates a peak-cancelled signal430.

Referring to FIG. 4A, the initial signal 410 includes 4 peaks 414-1 to414-4 exceeding a threshold 412. The peak #1 414-1 is detected and issuccessfully accepted. Accordingly, as shown in FIG. 4B, thecancellation pulse #1 420-1 is generated to cancel the peak #1 414-1.The cancellation pulse #1 420-1 is generated in such a manner that timealignment is maintained with respect to the peak #1 414-1. However,since the peak #2 414-2 appears within a processing time of the peak #1414-1, the peak #2 414-2 is ignored. In other words, since thecancellation pulse #1 420-1 for the peak #1 414-1 is not completelygenerated yet, the peak #2 414-2 cannot be accepted.

When the processing time (e.g., a time of N samples) of the cancellationpulse #1 420-1 elapses, a CPG may be open again to process another peak.Accordingly, the peak #3 414-3 is accepted, and the cancellation pulse#2 420-2 for the peak #3 414-3 is generated. However, since the peak #4414-4 is generated again within a processing time of N samples after thepeak #3 414-3, the peak #4 414-4 is ignored. That is, although the 4peaks 414-1 to 414-4 are generated, only the two cancellation pulses420-1 and 420-2 are generated.

As a result, since only the two cancellation pulses 420-1 and 420-2 aresubtracted from the initial signal 410, as shown in FIG. 4C, the peak #1414-1 and the peak #3 414-3 are cancelled. However, since cancellationpulses for the peak #2 414-2 and the peak 34 414-4 are not generated,the peak #2 414-2 and the peak #4 414-4 are still maintained without aloss.

As described above, when peaks are generated continuously, not all peakscan be cancelled since the cancellation pulse cannot be generated asfrequently as an interval of the peaks. As one solution for cancellingall of the peaks, a plurality of CPGs for generating the cancellationpulse are provided. However, this may require an increase in hardwareresources in quantity, and eventually may cause a cost increase.Accordingly, the present invention proposes various exemplaryembodiments capable of cancelling all of the peaks without an increaseof the CPG.

According to the various exemplary embodiments of the present invention,a processing time of the CPG is reduced. As described above, in order togenerate the cancellation pulse, the CPG multiplies coefficients of anoise shaping filter by a complex gain. The cancellation pulse has thesame length as the noise shaping filter. A task is not complete untilthe end of the multiplication performed on all of the coefficients, andthis shows a relation between the processing time of the CPG and thelength of the cancellation pulse. When the length of the noise shapingfilter is reduced, the processing time will be reduced, but this leadsto a deterioration of signal quality.

FIG. 5 illustrates a characteristic of a base waveform for acancellation pulse in a wireless communication system according to anexemplary embodiment of the present invention. The base waveform may bereferred to as a ‘noise shaping filter’.

Referring to FIG. 5, a base waveform 520 consists of N samples. Aspecific waveform of the base waveform 520 is pre-defined according to asignal characteristic of a system. The base waveform 520 is divided intoa first part 502 and a second part 504, by a maximum value. The firstpart 502 may be referred to as a ‘first half of the cancellation pulse’,and the second part 504 may be referred to as a ‘second half of thecancellation pulse’.

As shown in FIG. 5, the first part 502 and the second part 504 have asymmetry property. In other words, the first part 502 and the secondpart 504 are symmetric to each other. However, the first part 502 andthe second part 504 have a conjugate relation. As a result, coefficientsof each sample belonging to the first part 502 and coefficients of eachsample belonging to the second part 504 are identical in reverse order,except for a conjugate operation. The conjugate operation implies thatan imaginary component of a complex number is inverted.

By using the symmetry property of the base waveform for the cancellationpulse described above with reference to FIG. 5, a transmission deviceaccording to the exemplary embodiment of the present invention maysimultaneously generate the first half and second half of thecancellation pulse. Specifically, a method of generating thecancellation pulse according to the exemplary embodiment of the presentinvention may include two steps.

In a first step, a half of the noise shaping filter is multiplied by acomplex gain. In this case, a multiplication result of the noise shapingfilter and the complex gain is generated, and at the same time, amultiplication result of the conjugated noise shaping filter and thecomplex gain is generated. Herein, the multiplication result of thenoise shaping filter and the complex gain is the first half of thecancellation pulse, and the multiplication result of the conjugatednoise shaping filter and the complex gain is the second half of thecancellation pulse. However, coefficients belonging to the second halfare generated in reverse order. In this case, the second half generatedin reverse order is stored in a memory buffer. In a second step, valuesstored in the memory buffer are output in an order opposite to an inputorder. Accordingly, the second half of the cancellation pulse is finallygenerated.

FIG. 6 illustrates generating of a cancellation pulse by using a memorybuffer in a wireless communication system according to an exemplaryembodiment of the present invention.

Referring to FIG. 6, the aforementioned transmission device generates afirst half 622 of a cancellation pulse through scaling based on acomplex gain corresponding to a magnitude of a detected peak, performs aconjugate operation on coefficient values belonging to the first half,and thereafter stores a result thereof in a memory buffer 640.Thereafter, the transmission device outputs the coefficient values inreverse order from the memory buffer 640. Herein, the conjugateoperation may be performed when stored in the memory buffer 640. Asecond half 624 is delayed by a proper time for which a concatenationpoint is matched to the first half 622. Thereafter, an entirecancellation pulse 620 may be obtained by concatenating the first half622 and the second half 624. Since the memory buffer 640 performs anoutput in reverse order of input, it may be referred to as a Last InFirst Output (LIFO) memory, and may be implemented by using a stack.

As shown in FIG. 6, by using the memory buffer, scaling for generatingthe second half of the cancellation pulse, that is, multiplicationoperations of the complex gain, may be excluded. Accordingly, aprocessing delay for generating the cancellation pulse is halved. Forexample, the processing delay is a half of a cancellation pulse length(a time of N/2 samples). Therefore, even if a different peak isgenerated within a processing time of N samples after peak detection,the transmission device may process the different peak.

A cancellation pulse generation means for generating a cancellationpulse according to the principle of FIG. 6 may be configured as shown inFIG. 7 described below. FIG. 7 illustrates a block diagram of a meansfor generating a cancellation pulse in a wireless communication systemaccording to an exemplary embodiment of the present invention. Aconfiguration of the CPG 320 of FIG. 3 is exemplified in FIG. 7.

Referring to FIG. 7, the cancellation pulse generation means includes ascaling and conjugate unit 710, a first buffering unit 722, a secondbuffering unit 724, and adders 732 and 734.

The scaling and conjugate unit 710 scales a base waveform of thecancellation pulse according to a complex gain corresponding to amagnitude of a detected peak. A specific value of the base waveform ispre-defined according to a signal characteristic of a system. In thiscase, according to the exemplary embodiment of the present invention,the base waveform includes only a part corresponding to a first half ofthe entire cancellation pulse. Further, the scaling and conjugate unit710 performs a conjugate operation on the scaled base waveform. Thescaled cancellation pulse is provided to the adders 732 and 734, and thescaled and conjugated cancellation pulse is provided to the firstbuffering unit 722 and the second buffering unit 724. The scaling isperformed by multiplying a value of the base waveform by the complexgain. Therefore, the scaling and conjugate unit 710 may be referred toas a ‘complex multiplier with conjugate’. In this case, according to theexemplary embodiment of the present invention, the scaling and conjugateunit 710 generates only the first half of the cancellation pulse. Sinceonly the first half is generated, the scaling and conjugate unit 710does not perform an operation for a second half. Therefore, the scalingand conjugate unit 710 may perform an operation for the cancellationpulse for a subsequent next peak.

The first buffering unit 722 generates the second half of thecancellation pulse for an I component. The first buffering unit 722stores sample values of the conjugated first half of the cancellationpulse provided from the scaling and conjugate unit 710 into a memory,and outputs the sample value in order opposite to a storing order. Thefirst buffering unit 722 may generate a second half of one cancellationsignal simultaneously by using a plurality of memory banks, and maystore a first half of another cancellation signal. For this, the firstbuffering unit 722 may include a switch #1, a switch #2, an LIFO memory#1, and an LIFO memory #2. The switch #1 and the switch #2 are providedfor conceptual meaning, and the first buffering unit 722 may perform aswitch function by changing an address for accessing the memory.Further, although the LIFO memory #1 and the LIFO memory #2 are shown asa plurality of memories physically separated, they may be configured asphysically one memory device.

The second buffering unit 724 generates the second half of thecancellation pulse for cancelling a Q component. The second bufferingunit 724 stores sample values of the conjugated first half of thecancellation pulse provided from the scaling and conjugate unit 710 intothe memory, and outputs the sample values in the order opposite to thestoring order. The second buffering unit 724 may generate the secondhalf of one cancellation signal simultaneously by using a plurality ofmemory banks and may store the first half of another cancellationsignal. For this, the second buffering unit 724 may include a switch #3,a switch #4, an LIFO memory #3, and an LIFO memory #4. The switch #3 andthe switch #4 are provided as conceptual meaning, and the secondbuffering unit 724 may perform a switch function by changing an addressfor accessing the memory. Further, although the LIFO memory #3 and theLIFO memory #4 are shown as a plurality of memories physicallyseparated, they may be configured as physically one memory device.

The adders 732 and 734 concatenate the first half of the cancellationpulse provided from the scaling and conjugate unit 710 and the secondhalf of the cancellation pulse provided from the first buffering unit722 and the second buffering unit 724. That is, the adders 732 and 734respectively correspond to an I component and a Q component, andgenerate the entire cancellation pulse by adding the second half afterthe first half.

When two peaks are generated continuously, an exemplary operation of thefirst buffering unit 722 and the second buffering unit 724 is asfollows. When the two peaks are generated continuously, two cancellationpulses are required continuously. Initially, the switch #1, the switch#2, the switch #3, and the switch #4 are respectively connected to theLIFO memory #1, the LIFO memory #2, the LIFO memory #3, and the LIFOmemory #4. Accordingly, when an I component and Q component of aconjugated first half of a first cancellation pulse is provided, the Icomponent is stored in the LIFO memory #1 and the Q component is storedin the LIFO memory #3, and no value is output. In an initial state,since there is no value stored in the LIFO memory #2 and the LIFO memory#4, no value is output through the switch #2 and the switch #4.

The first half of the first cancellation pulse is scaled by the scalingand conjugate unit 710, and thereafter a connection state of the switch#1, the switch #2, the switch #3, and the switch #4 is changed to beopposite. That is, the switch #1, the switch #2, the switch #3, and theswitch #4 are respectively connected to the LIFO memory #2, the LIFOmemory #1, the LIFO memory #4, and the LIFO memory #3. Accordingly,values stored in the LIFO memory #1 are output through the switch #2 inreverse order of input, and values stored in the LIFO memory #3 areoutput through the switch #4 in reverse order of input. Accordingly, asecond half of the first cancellation pulse is generated.

In this case, scaling starts for a first half of a second cancellationpulse. Accordingly, an I component and Q component of the conjugatedfirst half of the second cancellation pulse are provided. According to acurrent connection state of switches, during the second half of thefirst cancellation pulse is output, the I component is stored in theLIFO memory #2 and the Q component is stored in the LIFO memory #4, andno value is output. Thereafter, the connection state of the switches ischanged to be opposite, values stored in the LIFO memory #2 are outputthrough the switch #2 in reverse order of input, and values stored inthe LIFO memory #4 are output through the switch #4 in reverse order ofinput. Accordingly, a second half of the second cancellation pulse isgenerated.

FIG. 8 is a conceptual view illustrating a procedure of generating acancellation pulse in a wireless communication system according to anexemplary embodiment of the present invention. In FIG. 8, multiplicationoperations and summation operations with the structure of FIG. 7 areillustrated.

Referring to FIG. 8, multiplication is performed between a realcomponent 871 of a noise shaping filter and a real component 881 of acomplex gain, multiplication is performed between an imaginary component873 of the noise shaping filter and an imaginary component 883 of thecomplex gain, multiplication is performed between the real component 871of the noise shaping filter and the imaginary component 883 of thecomplex gain, and multiplication is performed between the imaginarycomponent 873 of the noise shaping filter and the real component 881 ofthe complex gain. Herein, the real component 871 of the noise shapingfilter and the imaginary component 873 of the noise shaping filterinclude only a first half of the entire cancellation pulse. A result ofthe multiplication between the real component 871 of the noise shapingfilter and the real component 881 of the complex gain is denoted by ‘A’.A result of the multiplication between the imaginary component 873 ofthe noise shaping filter and the imaginary component 883 of the complexgain is denoted by ‘B’. A result of the multiplication between the realcomponent 871 of the noise shaping filter and the imaginary component883 of the complex gain is denoted by ‘C’. A result of themultiplication between the imaginary component 873 of the noise shapingfilter and the real component 881 of the complex gain is denoted by ‘D’.Herein, the multiplication operation may include a conjugate operation.

Thereafter, a real component 891 of a first half is generated bysubtracting the multiplication result A and the multiplication result B.An imaginary component 893 of the first half is generated by adding themultiplication result C and the multiplication result D. A realcomponent 895 of a second half is generated by adding the multiplicationresult A and the multiplication result B. An imaginary component 897 ofthe second half is generated by subtracting the multiplication result Aand the multiplication result B.

When the cancellation pulse is generated by using the memory buffer asdescribed above, continuous peaks may be processed as shown in FIGS. 9Ato 9E described below.

FIGS. 9A to 9E illustrate another example of a result of processingcontinuous peaks in a wireless communication system according to anexemplary embodiment of the present invention.

Specifically, FIG. 9A illustrates an initial signal 910, FIG. 9Billustrates first halves 922-1 to 922-4 of a cancellation pulsegenerated by multiplication of a complex gain, FIG. 9C illustratessecond halves 924-1 to 924-4 of a cancellation pulse generated by aconjugate operation, FIG. 9D illustrates entire cancellation pulses920-1 to 920-4, and FIG. 9E illustrates a peak-cancelled signal 930.

Referring to FIG. 9A, the initial signal 910 includes 4 peaks 914-1 to914-4 exceeding a threshold 912. A transmission device detects the peak#1 914-1, and as shown in FIG. 9B, generates the first half 922-1 of acancellation pulse #1 for cancelling the peak #1 914-1. The first half922-1 of the cancellation pulse #1 includes N/2 samples. In this case,the first half 922-1 of the cancellation pulse #1 is stored in a memorybuffer. Further, as shown in FIG. 9C, the second half 924-1 of thecancellation pulse #1 is generated by being output from the memorybuffer. Accordingly, the cancellation pulse #1 920-1 may be generated asshown in FIG. 9D. That is, after the first half 922-1 of thecancellation pulse #1 is generated, a cancellation pulse generationmeans of the transmission device does not generate the second half 924-1of the cancellation pulse #1. Accordingly, the cancellation pulsegeneration means may operate for the next peak #2 914-2.

During the second half 924-1 of the cancellation pulse #1 is output fromthe memory buffer as shown in FIG. 9C, the transmission device generatesthe first half 922-1 of the cancellation pulse #2 for the peak #2 914-2as shown in FIG. 9B. The first half 922-2 of the cancellation pulse #2is stored in the memory buffer, and as shown in FIG. 9C, the second half924-2 of the cancellation pulse #2 is generated by being output from thememory buffer. Accordingly, the cancellation pulse #2 920-2 may begenerated as shown in FIG. 9D.

During the second half 924-2 of the cancellation pulse #2 is output fromthe memory buffer as shown in FIG. 9C, the transmission device generatesthe first half 922-3 of the cancellation pulse #3 for the peak #3 914-3as shown in FIG. 9B. The first half 922-3 of the cancellation pulse #3is stored in the memory buffer, and as shown in FIG. 9C, the second half924-3 of the cancellation pulse #3 is generated by being output from thememory buffer. Accordingly, the cancellation pulse #3 920-3 may begenerated as shown in FIG. 9D.

During the second half 924-3 of the cancellation pulse #3 is output fromthe memory buffer as shown in FIG. 9C, the transmission device generatesthe first half 922-4 of the cancellation pulse #4 for the peak #4 914-4as shown in FIG. 9B. The first half 922-4 of the cancellation pulse #4is stored in the memory buffer, and as shown in FIG. 9C, the second half924-4 of the cancellation pulse #4 is generated by being output from thememory buffer. Accordingly, the cancellation pulse #4 920-4 may begenerated as shown in FIG. 9D.

Through the aforementioned procedure, as shown in FIG. 9D, the fourcancellation pulses 920-1 to 920-4 are generated to cancel the fourpeaks 914-1 to 914-4. Accordingly, the four peaks 914-1 to 914-4 may beattenuated or cancelled to be below the threshold 912.

FIG. 10 illustrates a procedure of generating a cancellation pulse in awireless communication system according to an exemplary embodiment ofthe present invention. Hereinafter, an entity for generating thecancellation pulse is referred to as a CPG.

Referring to FIG. 10, the CPG initializes parameters and a memory instep 1001. The parameters includes ‘S’ for indicating a status of abinary switch, ‘m’ for indicating an index or address of the memory, and‘n’ for indicating a coefficient index of a noise shaping filter. Theswitch status S defines a direction for the memory index m. According toa value of the switch status S, a value of the memory index m may beincreased or decreased. When data is recorded, the memory index mproceeds in one direction, whereas when the data is extracted, thememory index m proceeds in an opposite direction. In the step 1001, theswitch status S is initialized to ‘1’, the memory index m is initializedto ‘0’, and the coefficient index ‘n’ is initialized to [N/2]. The N isthe number of coefficients of the noise shaping filter, that is, alength thereof, and is the same as a length of the cancellation pulse.The memory is for storing the second half of the cancellation pulse, andis divided into I_(M) for a real component and Q_(M) for an imaginarycomponent. I_(M)(m) denotes an m^(th) storage space of the memory forthe real component, and Q_(M)(m) denotes an m^(th) storage space of thememory for the imaginary component. Herein, the memory index m is aninteger number greater than or equal to 0 and less than or equal to[N/2]−1. The switch status S, the memory index m, and the memories I_(M)and Q_(M) implement an LIFO function. Next, when a rising edge of aclock cycle arrives, the CPG performs subsequent steps 1003 to 1041.That is, the subsequent steps 1003 to 1041 are performed one time inevery rising edge of the clock.

Proceeding to step 1003, the CPG determines whether the coefficientindex n is less than [N/2]+1. If the coefficient index n is not lessthan [N/2]+1, proceeding to step 1005, the CPG determines whether a peakis detected. If the peak is not detected, the CPG proceeds step 1011.Otherwise, if the peak is detected, proceeding to step 1007, the CPGdetermines a complex gain. The complex gain may be provided as a meansfor detecting the peak. Next, proceeding to step 1009, the CPG sets thecoefficient index n to ‘0’. Proceeding to step 1011, the CPG initializesa value of the first half and second half of the cancellation pulse to‘0’. In FIG. 10, a real component of the first half of the cancellationpulse is denoted by I₁, an imaginary component of the first half of thecancellation pulse is denoted by Q₁, a real component of the second halfof the cancellation pulse is denoted by I₂, and an imaginary componentof the second half of the cancellation pulse is denoted by Q₂. Next, theCPG proceeds to step 1025.

If the coefficient index n is less than [N/2]+1 in step 1003, proceedingto step 1013, the CPG reads an n^(th) coefficient of the noise shapingfilter. In FIG. 10, a real component of the n^(th) coefficient of thenoise shaping filter is denoted by I_(F)(n), and an imaginary componentof the n^(th) coefficient of the noise shaping filter is denoted byQ_(F)(n).

Next, proceeding to step 1015, the CPG determines an n^(th) coefficientof the first half of the cancellation pulse by using a complex gain andthe n^(th) coefficient of the noise shaping filter. In FIG. 10, a realcomponent of the complex gain is denoted by I_(G), and an imaginarycomponent of the complex gain is denoted by Q_(G). Specifically, the CPGmay determine the real component of the n^(th) coefficient of the firsthalf of the cancellation pulse by subtracting a product of the imaginarycomponent of the n^(th) coefficient of the noise shaping filter and theimaginary component of the complex gain from a product of the realcomponent of the n^(th) coefficient of the noise shaping filter and thereal component of the complex gain, and may determine the imaginarycomponent of the n^(th) coefficient of the first half of thecancellation pulse by adding a product of the real component of then^(th) coefficient of the noise shaping filter and the imaginarycomponent of the complex gain and a product of the imaginary componentof the n^(th) coefficient of the noise shaping filter and the realcomponent of the complex gain.

Next, proceeding to step 1017, the CPG determines the n^(th) coefficientof the second half of the cancellation pulse by using the complex gainand the n^(th) coefficient of the noise shaping filter. Specifically,the CPG may determine the real component of the n^(th) coefficient ofthe second half of the cancellation pulse by adding a product of theimaginary component of the n^(th) coefficient of the noise shapingfilter and the imaginary component of the complex gain from a product ofthe real component of the n^(th) coefficient of the noise shaping filterand the real component of the complex gain, and may determine theimaginary component of the n^(th) coefficient of the second half of thecancellation pulse by subtracting a product of the real component of then^(th) coefficient of the noise shaping filter and the imaginarycomponent of the complex gain and a product of the imaginary componentof the n^(th) coefficient of the noise shaping filter and the realcomponent of the complex gain.

Next, proceeding to step 1019, the CPG determines whether the n is equalto [N/2]. If the n is not equal to [N/2], the CPG proceeds to step 1023.Otherwise, if the n is equal to [N/2], proceeding to step 1021, the CPGtoggles the switch status S, and proceeds to step 1023. It should benoted that a toggled switch status S is not equivalent to the switchstatus S before toggling.

In step 1023, the CPG increases the coefficient index n by 1.

In step 1025, the CPG determines a CPG output by using a value stored ina memory and a complex multiplication result. In FIG. 10, a realcomponent of the CPG output is denoted by I_(OUT), and an imaginarycomponent of the CPG output is denoted by Q_(OUT). Specifically, the CPGmay determine the real component of the output by adding a value storedin an memory address m for the real component and the real component ofthe cancellation pulse, and may determine the real component of theoutput by adding a value stored in a memory address m for the imaginarycomponent and the imaginary component of the cancellation pulse.

Next, proceeding to step 1027, the CPG stores the second half of thecancellation pulse in the memory. Specifically, the CPG may store thereal component of the cancellation pulse to the memory address m for thereal component, and may store the imaginary component of thecancellation pulse to the memory address m for the imaginary component.

Next, proceeding to step 1029, the CPG confirms whether the switchstatus S is 1. If the switch status S is not 1, proceeding to step 1031,the CPG decreases the address index m by 1, and thereafter proceeding tostep 1033, determines whether the m is less than 0. If the m is not lessthan 0, the CPG returns to step 1003. Otherwise, if the m is less than0, proceeding to step 1035, the CPG sets the m to [N/2], and thereafterreturns to step 1003. If the switch status S is 1 in the step 1029,proceeding to step 1037, the CPG increases the address index m by 1, andthereafter proceeding to step 1039, determines whether the m is greaterthan [N/2]. If the m is not greater than [N/2], the CPG returns to thestep 1003. Otherwise, if the m is greater than [N/2], proceeding to step1041, the CPG sets the m to 0, and thereafter returns to the step 1003.

FIG. 11 illustrates a procedure of operating a transmission device in awireless communication system according to an exemplary embodiment ofthe present invention.

Referring to FIG. 11, the transmission device generates a first half ofa cancellation pulse corresponding to a magnitude of a peak in step1101. The cancellation pulse is a signal for cancelling or attenuating apeak detected from a transmission signal, and has a magnitudecorresponding to the magnitude of the peak. The magnitude of thecancellation pulse is determined according to a complex gaincorresponding to the magnitude of the peak. The first half is a part ofthe cancellation pulse. For example, the transmission device maygenerate the first half of the cancellation pulse by multiplying apre-defined base waveform of the cancellation pulse by the complex gain.

For example, the transmission device may determine a real component ofeach coefficient of the first half of the cancellation pulse bysubtracting a product of an imaginary component of an n^(th) coefficientof the base waveform and an imaginary component of the complex gain froma product of a real component of the n^(th) coefficient of the basewaveform and a real component of the complex gain. Further, thetransmission device may determine an imaginary component of eachcoefficient of the first half of the cancellation pulse by adding aproduct of a real component of each coefficient and the imaginarycomponent of the complex gain and a product of the imaginary componentof the base waveform and the imaginary component of the complex gain.

Next, proceeding to step 1103, the transmission device generates thesecond half from the first half on the basis of the symmetric propertyof the base waveform for the cancellation pulse. The second half impliesa part remaining after excluding a part corresponding to the first halffrom the cancellation pulse. The cancellation pulse has a bilateralsymmetry property by a maximum value, and in this case, the first halfand the second half have a conjugate relation, in other words, arelation in which an imaginary component has an opposite sign.Therefore, the transmission device may generate the second half byapplying a conjugation operation to coefficients belonging to the firsthalf and by sorting them in reverse order.

According to one exemplary embodiment of the present invention, thetransmission device may perform the conjugate operation by changing asign of an imaginary component of coefficients belonging to the firsthalf. According to another exemplary embodiment of the presentinvention, the transmission device may determine the conjugatedcoefficients directly from the base waveform and the complex gain. Forexample, the transmission device may determine a real component of eachcoefficient of the second half of the cancellation pulse by adding aproduct of a real component of each coefficient of the base waveform andan imaginary component of the complex gain and a product of an imagecomponent of each coefficient of the base waveform and an imaginarycomponent of the complex gain. Further, the transmission device maydetermine an imaginary component of each coefficient of the second halfof the cancellation pulse by subtracting a product of an imaginarycomponent of each coefficient of the base waveform and an imaginarycomponent of the complex gain and a product of an image component ofeach coefficient of the base waveform and a real component of thecomplex gain.

Thereafter, proceeding to step 1105, the transmission device cancels thepeak from the transmission signal. That is, the transmission devicecancels the peak by subtracting the cancellation pulse from thetransmission signal. For this, the transmission device may match thecancellation pulse to a position of the peak on a time axis. Forexample, the transmission device may delay the transmission signal by aprocessing time for generating the cancellation pulse.

Although not shown in FIG. 11, the transmission device may detect thepeak from the transmission signal, measure a magnitude of the peak, andthereafter determine a complex gain corresponding to the magnitude. Thecomplex gain is used when the cancellation pulse is generated.

In the example shown in FIG. 11, the transmission device sorts thecoefficients belonging to the first half in reverse order to generatethe second half of the cancellation pulse. Herein, the reverse-ordersorting may be performed by using a memory buffer. That is, thereverse-order sorting may be performed by using a stack-type memorywhich outputs data in an order opposite to an input order. For this, instep 1101, the transmission device may store the coefficients into thememory whenever each of the coefficients belonging to the first half isdetermined. In this case, according to one exemplary embodiment of thepresent invention, the transmission device may perform the conjugateoperation on the coefficients before being stored in the memory.According to another exemplary embodiment of the present invention, thetransmission device may perform the conjugate operation after extractingthe coefficients from the memory.

FIG. 12 illustrates a block diagram of a transmission device in awireless communication system according to an exemplary embodiment ofthe present invention. The structure exemplified in FIG. 12 is a part ofthe transmission device, and may be included as a part of a means forprocessing a digital signal.

Referring to FIG. 12, the transmission device includes a peak detector1210, a cancellation pulse generator 1220, and a peak cancelling unit1230.

The peak detector 1210 may detect a peak from a transmission signal,measure a magnitude of the peak, and thereafter determine a complex gaincorresponding to the magnitude. The complex gain is used when thecancellation pulse is generated. Therefore, the peak detector 1210provides the complex gain to the cancellation pulse generator 1220.

The cancellation pulse generator 1220 generates a cancellation pulse forcancelling the peak. A specific waveform of the cancellation pulse ispre-defined according to a signal characteristic of a system. That is,the cancellation pulse generator 1220 pre-stores a base waveform of thecancellation pulse, and generates the cancellation pulse correspondingto the peak from the base waveform according to a complex gain providedfrom the peak detector 1210. According to one exemplary embodiment, thecancellation pulse generator 1220 generates a part of the cancellationpulse by using the base waveform and the complex gain, and generates theremaining parts on the basis of a symmetry property of the base waveformfor the cancellation pulse. For example, the cancellation pulsegenerator 1220 may generate a first half of the cancellation pulse bymultiplying the base waveform and the complex gain, and may generate asecond half by performing a conjugation operation and reverse-ordersorting on coefficients belonging to the first half. The reverse-ordersorting may be performed by using a stack-type memory which outputs datain an order opposite to an input order. For this, the cancellation pulsegenerator 1220 may include at least one memory. In this case, thecancellation pulse generator 1220 may store the coefficients into thememory whenever each of the coefficients belonging to the first half isdetermined. In this case, according to one exemplary embodiment of thepresent invention, the cancellation pulse generator 1220 may perform theconjugate operation on the coefficients before being stored in thememory. According to another exemplary embodiment of the presentinvention, the cancellation pulse generator 1220 may perform theconjugate operation after extracting the coefficients from the memory.

The peak cancelling unit 1230 cancels or attenuates the peak from thetransmission signal. For example, the peak cancelling unit 1230 maycancel the peak by subtracting the cancellation pulse from thetransmission signal. For this, the peak cancelling unit 1230 may includeat least one subtractor. In addition, the peak cancelling unit 1230 mayfurther include a delay component to match the cancellation pulse to aposition of the peak on a time axis.

Although not shown in FIG. 12, the transmission device may furtherinclude at least one amplifier for amplifying the peak-cancelledtransmission signal. In addition, the transmission device may furtherinclude a Digital-to-Analog Converter (DAC) for converting a digitalsignal to an analog signal.

FIG. 13 illustrates a simulation experiment result of a method ofreducing a PAR according to an exemplary embodiment of the presentinvention. In FIG. 13, a Complementary Cumulative Distribution Function(CCDF) is shown depending on a PAR change of a signal. In FIG. 13, theCCDF is expressed in a log scale. A 4-stage structure in which 4 peakcancellation means are connected is shown in the simulation experimentresult of FIG. 13.

In FIG. 13, ‘with buffer’ implies a case where a cancellation pulse isgenerated by using a symmetry property, and ‘without buffer’ implies acase where the entire cancellation pulse is generated throughmultiplication of a base waveform and a complex gain. A chain lineindicates performance in case of having two CPGs without the buffer. Adotted line indicates performance in case of having two CPGs with thebuffer. A solid line indicates performance in case of having 4 CPGswithout the buffer.

Referring to FIG. 13, it is confirmed that performance is superior whenthe buffer is used. In case of using the buffer, although only two CPGsare provided, it is confirmed that performance is similar to a case ofhaving 4 CPGs. In case of having the 4 CPGs, since the number ofrequired multipliers is two times the case of having the 2 CPGs, it isconfirmed that performance is much superior when using the buffer.

In addition to the CCDF measurement result, a comparison result of acase of using a symmetry property and a case of not using the symmetryproperty is as follows.

First, a base waveform to be stored, that is, a length of a noiseshaping filter, is halved. This implies that a delay is decreased when acancellation pulse is generated. Second, additional LIFO memory blocksfor reversing an order of a conjugated control pulse are required.Third, a complex multiplier for providing a conjugate operation and amultiplication operation has a different structure.

In summary, in case of using the symmetry property, a processing time ofa CPG is decreased by ½, but an additional multiplier is not required.Further, due to an improved processing delay, the number of CPG unitsmay be decreased.

Methods based on the embodiments disclosed in the claims and/orspecification of the present invention can be implemented in hardware,software, or a combination of both.

When implemented in software, computer readable recording medium forstoring one or more programs (i.e., software modules) can be provided.The one or more programs stored in the computer readable recordingmedium are configured to be executed by one or more processors in anelectronic device. The one or more programs include instructions forallowing the electronic device to execute the methods based on variousexemplary embodiments disclosed in the claims and/or specification ofthe present invention.

The program (i.e., the software module or software) can be stored in arandom access memory, a non-volatile memory including a flash memory, aRead Only Memory (ROM), an Electrically Erasable Programmable Read OnlyMemory (EEPROM), a magnetic disc storage device, a Compact Disc-ROM(CD-ROM), Digital Versatile Discs (DVDs) or other forms of opticalstorage devices, and a magnetic cassette. Alternatively, the program canbe stored in a memory configured in combination of all or some of thesestorage media. In addition, the configured memory may be plural innumber.

Further, the program can be stored in an attachable storage devicecapable of accessing the electronic device through a communicationnetwork such as the Internet, an Intranet, a Local Area Network (LAN), aWide LAN (WLAN), or a Storage Area Network (SAN) or a communicationnetwork configured by combining the networks. The storage device canaccess the electronic device via an external port. In addition, anadditional storage unit on a communication network can access a devicefor performing an exemplary embodiment of the present invention.

In the aforementioned specific example embodiments of the presentinvention, a constitutional element included in the invention isexpressed in a singular or plural form according to the specific exampleembodiment proposed herein. However, the singular or plural expressionis selected properly for a situation proposed for the convenience ofexplanation, and thus the various exemplary embodiments of the presentinvention are not limited to a single or a plurality of constitutionalelements. Therefore, a constitutional element expressed in a plural formcan also be expressed in a singular form, or vice versa.

While the present invention has been shown and described with referenceto certain preferred embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the presentinvention as defined by the appended claims. Therefore, the scope of thepresent invention is defined not by the detailed description thereof butby the appended claims, and all differences within equivalents of thescope will be construed as being included in the present invention.

The invention claimed is:
 1. A method for operating a transmissiondevice in a wireless communication system, the method comprising:detecting a first peak and a second peak of an original signal;generating, based on a complex gain of the first peak of the originalsignal, a first portion of a first cancelling pulse for attenuating thefirst peak; storing coefficients corresponding to the first portion ofthe first cancelling pulse in an order; generating a second portion ofthe first cancelling pulse by outputting the stored coefficients in areverse order with respect to the order, during a process in whichcoefficients corresponding to a first portion of a second cancellingpulse for attenuating the second peak are stored; and generating atransmission signal by applying the first cancelling pulse and thesecond cancelling pulse to the original signal.
 2. The method of claim1, wherein detecting the first peak and the second peak comprises:receiving the original signal; and detecting the first peak and thesecond peak of the original signal by comparing a value of magnitude forthe original signal and a threshold value.
 3. The method of claim 2,wherein generating the first portion of the first cancelling pulsecomprises: determining the complex gain based on the magnitude of thedetected first peak of the original signal; and multiplying the complexgain by a base waveform including a plurality of samples withcoefficients.
 4. The method of claim 2, wherein the complex gain isproportional to the magnitude of the first peak.
 5. The method of claim1, wherein the first cancelling pulse is divided into the first portionand the second portion at a maximum value, wherein the second portion isa portion of the first cancelling pulse, except for the first portion ofthe first cancelling pulse, wherein the first portion of the firstcancelling pulse is followed by the second portion of the firstcancelling pulse, and wherein the second portion of the first cancellingpulse is identical to a conjugate of the first portion of the firstcancelling pulse.
 6. An apparatus for a transmission device in awireless communication system, the apparatus comprising: at least onememory; a peak detector configured to detect a first peak and a secondpeak of an original signal; a generator configured to: generate, basedon a complex gain of the first peak of the original signal, a firstportion of a first cancelling pulse for attenuating the first peak,store coefficients corresponding to the first portion of the firstcancelling pulse in an order, and generate a second portion of the firstcancelling pulse by outputting the stored coefficients in a reverseorder with respect to the order during a process in which coefficientscorresponding to a first portion of a second cancelling pulse forattenuating the second peak is stored; and a cancelling unit, whichincludes at least one subtractor, configured to generate a transmissionsignal by applying the first cancelling pulse and the second cancellingpulse to the original signal.
 7. The apparatus of claim 6, wherein thepeak detector is further configured to: receive the original signal; anddetect the first peak and the second peak of the original signal bycomparing a value of magnitude for the original signal and a thresholdvalue.
 8. The apparatus of claim 7, wherein the generator is furtherconfigured to: determine the complex gain based on the magnitude of thedetected first peak of the original signal; and multiply the complexgain by a base waveform including a plurality of samples.
 9. Theapparatus of claim 7, wherein the complex gain is proportional to themagnitude of the first peak.
 10. The apparatus of claim 6, wherein thefirst cancelling pulse is divided into the first portion and the secondportion at a maximum value, wherein the second portion is a portion ofthe first cancelling pulse, except for the first portion of the firstcancelling pulse, wherein the first portion of the first cancellingpulse is followed by the second portion of the first cancelling pulse,and wherein the second portion of the first cancelling pulse isidentical to a conjugate of the first portion of the first cancellingpulse.